Blog Posts by Steve Souders

In The Importance of Front-End Performance, I reveal that 80% of the end-user response time is spent on the front-end. Most of this time is tied up in downloading all the components in the page: images, stylesheets, scripts, Flash, etc. Reducing the number of components in turn reduces the number of HTTP requests required to render the page. This is the key to faster pages.

One way to reduce the number of components in the page is to simplify the page's design. But is there a way to build pages with richer content while also achieving fast response times? Here are some techniques for reducing the number of HTTP requests, while still supporting rich page designs.

Image maps combine multiple images into a single image. The overall size is about the same, but reducing the number of HTTP requests speeds up the page. Image maps only work if the images are contiguous in the page, such as a navigation bar. Defining the coordinates of image maps can be tedious and error prone.

In 2004, I started the Exceptional Performance group at Yahoo!. We're a small team chartered to measure and improve the performance of Yahoo!'s products. Having worked as a back-end engineer most of my career, I approached this as I would a code optimization project - I profiled web performance to identify where there was the greatest opportunity for improvement. Since our goal is to improve the end-user experience, I measured response times in a browser over various bandwidth speeds. What I saw is illustrated in the following chart showing HTTP traffic for http://www.yahoo.com.

In the figure above, the first bar, labeled "html", is the initial request for the HTML document. In this case, only 5% of the end-user response time is spent fetching the HTML document. This result holds true for almost all web sites. In sampling the top ten U.S. websites, all but one spend less than 20% of the total response time getting the HTML document. The other 80+% of the time is spent dealing with